1. Field of the Invention
The teachings of the present invention relates to an electric actuator system for driving a movable member of an air conditioning system for vehicle such as an air mix door and an air-outlet mode switching door.
2. Description of the Related Art
Generally, a conventional electric actuator system is known that rotates an electric actuator (for example, a DC motor) to a limit, where the rotation is restricted by mechanical regulation means such as a stopper, and then stores the rotation limit point to control an angle of rotation of a rotating shaft. Hereinafter, the operation of rotating the electric actuator to the position of the origin and then storing the rotation of the electric actuator to the position of the origin is referred to as “origin position setting.”
In this electric actuator system, a lever is secured to the rotating shaft. When the lever strikes against the stopper to operate the electric actuator to the point of the limit of rotation, the stopper bends. It was found that the angle of rotation cannot be accurately controlled because a variation occurs in the position of the origin as a result of the bend.
Therefore, the inventors of the present invention have examined the use of a pulse generator instead of the mechanical regulation means, such as a stopper, in order to detect the position of the origin. The pulse generator generates a pulse signal in an initialization pattern that indicates the position of the origin when a DC motor functioning as the electric actuator rotates to the point of the limit of rotation.
Hereinafter, the pulse generator will be described with reference to FIGS. 12 and 13. A pulse pattern plate 153, which rotates cooperatively with an output shaft 127 with the rotation of a DC motor, is used. The pulse pattern plate 153 is provided with first and second pulse patterns 151, 152, and a common pattern 154.
As shown in FIG. 12, the first pulse pattern 151 is composed of a conductive part 151a and a non-conductive part 151b, which are alternately arranged in a circumferential direction. The second pulse pattern 152 is composed of a conductive part 152a and a non-conductive part 152b, which are alternately arranged in a circumferential direction. The common pattern 154 is composed of conductive parts 154a and a non-conductive part 154b, which are arranged in a circumferential direction.
As shown in FIG. 13, in a circular rotation detection area 300 of the pulse pattern plate 153, an angle of circumference al of the conductive part 151a is set equal to an angle of circumference β1 of the non-conductive part 151b, whereas an angle of circumference α2 of the conductive part 152a is set equal to an angle of circumference β2 of the non-conductive part 152b. Moreover, a phase of the first pulse pattern 151 is shifted from that of the second pulse pattern 152 by about a half of each of the angle of circumference α1 and α2 (=each of the angles of circumference β1 and β2). The common pattern 154 in the area 300 is composed solely of the conductive part 154a. 
The rotation detection area 300 as described above is used to generate a pattern of a pulse signal used for detecting an angle of rotation (hereinafter, referred to as an angle detection pattern).
As shown in FIG. 13, in an area other than the area 300 of the pulse pattern plate 153, that is, in an initialization area 301, the first and second pulse patterns 151 and 152 are composed solely of the conductive parts 151a and 152a, respectively. In this area, the common pattern 154 is formed so that the non-conductive part 154b is interposed between the conductive parts 154a in a circumferential direction.
The initialization area 301 as described above is used to generate a pulse signal pattern that indicates the position of the origin (hereinafter, referred to as an initialization pattern). In the first and second pulse patterns 151 and 152 and the common pattern 154, the respective conductive parts are electrically connected with each other. Furthermore, a first contact brush 155 and a second contact brush 156 (electric contacts), each being made of a copper conductive material, are used so as to be connected to a positive electrode (+) of a battery. A third contact brush 157 made of a copper conductive material is used so as to be connected to a negative electrode (−) of the battery. In this case, the first to third contact brushes 155 to 157 are arranged so that the first contact brush 155 is in contact with the first pulse pattern 151, the second contact brush 156 is in contact with the second pulse pattern 152, and the third contact brush 157 is in contact with the common pattern 154.
Next, an electric control circuit 200 for detecting a pulse generated-from the first and second pulse patterns 151 and 152 and the common pattern 154 will be described with reference to FIG. 14. First, a DC motor (M) rotates to cause the rotation of the output shaft 127 (the pulse pattern plate 153). When the first to third contact brushes 155 to 157 are in contact with the rotation detection area 300, the third contact brush 157 is in contact with the conductive part 154a. 
In this condition, a conducting (ON) state and a non-conducting (OFF) state alternately occur in a periodic manner. In the conducting state, the first and second contact brushes 155 and 156 on the positive electrode side (+) are in contact with the conductive parts 151a and 152a, respectively. On the other hand, in the non-conducing state, the first and second contact brushes 155 and 156 are in contact with the non-conductive parts 151b and 152b, respectively. Thus, since a pulse signal is generated in the first and second contact brushes 155 and 156 each time the DC motor 110 rotates at a predetermined angle, the CPU 240 counts the pulse signals through a pulse signal detection circuit 220 to enable the detection of an angle of rotation of the output shaft 127.
Furthermore, when the DC motor 110 rotates to cause the rotation of the output shaft 127 (the pulse pattern plate 153) so that the first to third contact brushes 155 to 157 are brought into contact with the initialization area 301, the conducting (ON) state, where the first and second contact brushes 155 and 156 are respectively in contact with the conductive parts 151a and 152a, is maintained. Meanwhile, the third contact brush 157 and the common pattern 154 transit from the conductive (ON) state where the third contact brush 157 and the conductive part 154a are in contact with each other, through the non-conductive state (OFF) where the third contact brush 157 and the non-conductive part 154b are in contact with each other, again to the conductive (ON) state where the third contact brush 157 and the conductive part 154a are in contact with each other (the conductive part→the non-conductive part→the conductive part).
Therefore, in the first and second contact brushes 155 and 156, two-phase pulse signals (A-phase and B-phase) in the initialization pattern are generated in accordance with the angular rotation of the DC motor 110 as follows. Incidentally, switching means 158c in FIG. 14 is composed of the brush 157, the conductive part 154a, and the non-conductive part 154b. In the same manner, switching means 158a is composed of the brush 155, the conductive part 151a and the non-conductive part 151b, whereas switching means 158b is composed of the brush 156, the conductive part 152a, and the non-conductive part 152b. 
More specifically, when the first to third contact brushes 155 to 157 are in contact with the initialization area 301, the conducting (ON) state where the first and second contact brushes 155 and 156 on the positive electrode side are in contact with the conductive parts 151a and 152a, is maintained (low-level signals “00” are maintained). Meanwhile, the third contact brush 157 on the negative electrode side and the common pattern 154 transit from the conductive (ON) state (low-level signals “00”) where the third contact brush 157 and the conductive part 154a are in contact with each other, through the non-conductive (OFF) state (the high-level signals “11”) where the third contact brush 157 and the non-conductive part 154b are in contact with each other, again to the conductive (ON) state (the low-level signals “00”) where the third contact brush 157 and the conductive part 154a are in contact with each other (the conductive part→the non-conductive part→the conductive part).
More specifically, the initialization pattern is not such that the respective amplitudes of the two-phase pulse signals are alternately switched but such that the amplitudes of the two-phase pulse signals are simultaneously switched from the low-level signal (“00”) to the high-level signal (“11”) and simultaneously switched from the high-level signal (“11”) to the low-level signal (“00”). Herein, “0” indicates a low-level signal and “1” indicates a high-level signal.
As described above, in contrast to the angle detection pattern used for detecting the angular rotation of the DC motor 110, the initialization pattern is such that the amplitudes of the two-phase pulse signals simultaneously change.
Then, when the CPU 240 detects the two-phase pulse signals in the initialization pattern through the pulse signal detection circuit 220, the power supply to the DC motor 110 is stopped by a motor driving circuit 210. This electrically regulates the rotation of the DC motor 110 and the position where the two-phase pulse signals in the initialization pattern are detected as the position of the origin is stored.
As is apparent from the above description, the pulse generator 158 including the switching means 158a to 158c for generating a pulse signal by the first to third contact brushes 155 to 157 and the pulse pattern plate 153 each time the output shaft 127 is rotated at a predetermined angle is configured.
Herein, as shown in FIG. 12, the present inventors have examined the cases where an operation range in the pulse pattern plate 153 in which the angle of rotation is controlled (that is, a control range of the angle of rotation) is formed to be in a horizontal, approximately symmetric, fan-like shape including the initialization area 301 as a center. Further, they have also examined that the angle of rotation is controlled by rotating the pulse pattern plate 153 only in a first operating direction at the initialization. Then, it is found that the following inconvenience occurs.
More specifically, suppose a case in which the first to third contact brushes 155 to 157 stop in a contact state in the initialization area 301 and an area on the right of the initialization area 301 within the operation range of the pulse pattern plate 153 in FIG. 12. In this case, an area where the origin position setting is impossible (hereinafter, referred to as an origin position setting NG stop range) is generated. For example, once the first to third contact brushes 155 to 157 are stopped in contact with the initialization area 301, the first to third contact brushes 155 to 157 never reach the initialization area 301 unless the pulse pattern plate 153 is rotated at 360 degrees even if the pulse pattern plate 153 is rotated in the first operating direction in order to control the angle of rotation.
Similarly, once the first to third contact brushes 155 to 157 stop in the area within the operation range on the right of the initialization area 301 in FIG. 12, the first to third contact brushes 155 to 157 never reach the initialization area 301 unless the pulse pattern plate 153 is rotated at 360 degrees. This is such even if the pulse pattern plate 153 is rotated in the first operating direction in order to control the angle of rotation.
In this case, if a movable member (for example, an air mix door, an air-outlet mode switching door and the like) is to be driven by the rotation of the output shaft 127, it is considered that it is impossible to rotate the pulse pattern plate 153 360 degrees in some cases depending on the structure of a link mechanism for linking the output shaft 127 and the movable member with each other. On the other hand, even if the pulse pattern plate 153 is formed to be rotatable 360 degrees in view of the structure of the link mechanism, the movable member is not necessarily rotated at 360 degrees even if the pulse pattern plate 153 is rotated at 360 degrees.
For example, in the case where the movable member is formed to rotate at 90 degrees when the pulse pattern plate 153 is rotated at 360 degrees, two-phase pulse signals in the initialization pattern are generated when the pulse pattern plate 153 is rotated at 360 degrees. However, the movable member does not reach the normal position of the origin.
As described above, when the first to third contact brushes 155 to 157 stop within the origin position setting NG stop range in a contact state, a pulse signal in the initialization pattern may not be generated or the movable member may not reach the normal position of the origin to prevent the detection of the position of the origin. As a result, there is a possibility that the origin position setting cannot be completed.